Evaluation of the impact of different sewage treatment processes on shellfishery pollution using a geographic information system (GIS)

Filter-feeding bivalve molluscs such as oysters, clams, mussels and cockles can concentrate microorganisms, including pathogens, from contaminated wat ers. Consumption of shellfish contaminated by human sewage may then result in illness such as viral gastroenteritis or infectious hepatitis. Under the EC Shellfish Hygiene Directive (91/492/EEC) controls are placed on the com mercial harvesting of shellfish from such areas in order to reduce the risk of infection. Reduction of contamination should result in a reduction of t he risk of illness and should also increase the commercial potential of har vesting areas. Predicting the effect of change in sewage treatment type on the extent of contamination of nearby shellfisheries is more difficult than predicting the effect on water quality. A geographic information system (G IS) was used to relate microbiological data obtained from shellfish monitor ing to the type and size of sewage discharges in the vicinity of harvesting areas. Data extracted using the GIS were further analysed using a statisti cal software package. The generic relationships obtained using this method were tested against shellfish monitoring data obtained from the vicinity of individual sewage improvement schemes. The results are discussed in relati on to the most appropriate policy for capital investment on discharge schem es impacting molluscan shellfisheries. (C) 1998 Published by Elsevier Scien ce Ltd on behalf of the IAWQ. All rights reserved.